Cutaneous accumulation of abnormal polyglutamine proteins of patients with dentatorubral-pallidoluysian atrophy

BACKGROUND AND PURPOSE

Dentatorubral-pallidoluysian atrophy (DRPLA) is a hereditary spinocerebellar degeneration caused by expansion of a trinucleotide CAG repeat encoding a polyglutamine tract in a disease protein atrophin-1. The clinical features include ataxia, choreoathetosis, and dementia, which result from neural degeneration caused by the mutant atrophin-1.

METHODS

We performed skin biopsy in two patients with DRPLA.

RESULTS

We found multiple clear cells in the epidermis, which were positive for proteins containing an expanded polyglutamine stretches. The clear cells were p63 (+), S-100 (-), and cytokeratin 20 (-), showing that they were keratinocytes. Negative or weak signals of pan-cytokeratin were consistent with the finding of decreased tonofilaments at the electron microscopic level.

CONCLUSIONS

The presence of clear keratincoytes showed that the mutant proteins interfered in cellular functions not only in neural cells but also in keratinocytes. The skin is accessible by biopsy, making it important in the diagnosis. Furthermore, the polyglutamine staining in the skin may be useful for evaluation of therapeutic modalities for DRPLA and other polyglutamine diseases.

Profiles of Foxp3+ regulatory T cells in eczematous dermatitis, psoriasis vulgaris and mycosis fungoides

BACKGROUND

It is well known that regulatory T cells (Tregs), identified by their expression of CD4, CD25 and Foxp3, play a crucial role in maintaining peripheral tolerance. Recently, it has been demonstrated that a Treg population resides in normal human skin. However, only a few studies have demonstrated the presence of Foxp3+ Tregs in inflammatory skin disorders.

OBJECTIVES

In this study, we immunohistologically examined the presence of CD4+ CD25+ Foxp3+ Tregs in the lesional skin of psoriasis vulgaris, mycosis fungoides and eczematous dermatitis.

METHODS

We used immunohistochemistry to examine the presence of Foxp3+ Tregs in fixed sections of the lesional skin from 16 patients with psoriasis vulgaris, 17 patients with mycosis fungides and 18 patients with eczematous dermatitis in addition to 10 normal skin samples.

RESULTS

In normal skin, epidermal and dermal Foxp3+ cells were rare. The psoriasis vulgaris, mycosis fungoides and eczematous dermatitis samples contained substantial numbers of epidermal and dermal CD3+, CD4+ and CD25+ Foxp3+ Tregs. The epidermis contained a higher percentage of CD3+, CD4+ and CD25+ Foxp3+ cells than the dermis. The percentage of Foxp3+ cells among CD3+ or CD4+ cells was significantly lower in eczematous dermatitis than in psoriasis vulgaris or mycosis fungoides, and that of dermal Foxp3+ cells was significantly lower in psoriasis vulgaris than in eczematous dermatitis or mycosis fungoides.

CONCLUSIONS

The lower percentage of epidermal or dermal Foxp3+ cells in eczematous dermatitis or psoriasis vulgaris, respectively, might contribute to their pathogenesis.

p51/p63 Inhibits ultraviolet B-induced apoptosis via Akt activation

The epidermis must be protected against excess apoptotic cell death in response to ultraviolet-B (UV-B) irradiation. p53 is known to be critical for this protection. Although the p53 family member DeltaNp51B/DeltaNp63alpha (an N terminal-deleted form of p51/p63) is abundantly expressed in keratinocytes, its contribution to UV-B-dependent apoptosis is largely unknown. We found that, after a transient increase, DeltaNp51B is downregulated in UV-B-irradiated keratinocytes undergoing apoptosis, whereas p53 is upregulated with delayed kinetics. Furthermore, the reduction of DeltaNp51B by small interfering RNAs augmented UV-B-dependent apoptosis in keratinocytes, indicating that DeltaNp51B blocks keratinocyte apoptosis. Although the exogenous expression of DeltaNp51B in keratinocytes did not further block the UV-B-dependent apoptosis, to our surprise the expression of TAp51B (an isoform with a full NH(2)-terminal transactivation domain that is structurally and functionally similar to p53) decreased apoptosis significantly. The blockade of keratinocyte apoptosis by the p51 was dependent on the phosphorylation of Akt, resulting in the activation of a survival pathway. Thus, in addition to its indispensable roles in epithelial development, p51 acts in adult cells to protect the epidermis against UV-B irradiation by preventing excess depletion of keratinocytes.

p53 homologue, p51/p63, maintains the immaturity of keratinocyte stem cells by inhibiting Notch1 activity

p53 homologue, p51/p63, predominantly expressed in keratinocyte stem cells, is indispensable for the formation of epidermis. Notch1, another such gene indispensable for the process, induces growth arrest and differentiation in keratinocytes. We found that exogenous expression of DeltaNp51B (DeltaNp63alpha), one of the isoforms of p51 specifically expressed in basal keratinocytes, blocked Notch 1-dependent growth arrest and differentiation in mouse keratinocytes by inhibiting p21 expression and maintaining integrins expression. Furthermore, DeltaNp51B by itself was found to have ability to induce expression of integrin alpha6beta4, which promotes attachment of basal cells to basal membrane thereby keeping the cells in immature state. Therefore, we conclude that DeltaNp51B expression warrants integrin expression even under the influence of Notch1 and that DeltaNp51B is a long-sought factor required to maintain basal cell keratinocytes immaturity by inhibiting Notch1 activity. We will postulate a plausible model explaining the maintenance of the squamous epithelium architectures as well as offering mechanistic explanations for pathological features of skin diseases, including cancers, psoriasis along with physiological wound healings.

Effects of heat stress and mechanical stretch on protein expression in cultured skeletal muscle cells

Effects of heat stress, mechanical stretching or a combination of both on the expression of heat shock proteins (HSPs) and total protein level were studied in a culture system. Rat skeletal muscle cells (L6) were cultured on flexible-bottomed culture plates. They were subjected to one of the four following conditions: (1) 97 h incubation at 37 degrees C, (2) 1 h incubation at 41 degrees C followed by 96 h incubation at 37 degrees C, (3) 1 h incubation at 37 degrees C followed by 96 h cyclic stretching (18% of initial length, 2-s stretch and 4-s release) at 37 degrees C or (4) 1 h incubation at 41 degrees C followed by 96 h cyclic stretching at 37 degrees C. The expression of HSP72 and HSP90 and total protein was determined in the crude homogenates, supernatant and pellets. Cellular protein concentrations in the homogenates and pellets were increased by heat stress and/or mechanical stress (stretch). A cumulative effect of the combination of heating and stretch on the protein concentration in the homogenates and in the pellets was noted. The expressions of HSP72 and HSP90 in the pellets were also increased by heat stress and/or stretch. However, HSP90 in the supernatant did not change following heat stress and/or stretch. The regulation of HSP72 and HSP90 expression in skeletal muscle cells may be closely related to total protein, the abundance of which is also stimulated by mechanical and heat stresses. These observations suggest strongly that heating and passive stretch of muscle may be useful as a means of increasing muscle mass, not only in athletes but also in patients during rehabilitation.

Molecular events occurring behind ultraviolet-induced skin inflammation

We reviewed a recent advance in the studies of the molecular mechanisms for 'ultraviolet responses', paying special attention to two transcription factors, nuclear factor kappa B and p53, and to a balance noted between an anti-apoptotic phosphatidylinositol 3-kinase-Akt pathway and its inhibitory ceramide-caveolin-1 pathway. These studies were mostly carried out using in vitro or animal models. On the basis of these results, we determined that phase by phase molecular events clarified in these studies correspond well with the three phases of ultraviolet-induced inflammation observed, i.e. the early vasodilatory phase, the second inflammatory phase in which many inflammatory cells such as neutrophils and T cells accumulate in the skin, and the last regressive phase based on several anti-inflammatory events.

Cytosolic O-GlcNAc accumulation is not involved in beta-cell death in HIT-T15 or Min6

O-linked N-acetylglucosamine (O-GlcNAc) is attached to and detached from proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase, respectively. It has been proposed that streptozotocin induces pancreatic beta-cell death by blocking O-GlcNAcase and increasing O-GlcNAc. To elucidate the relationship between cytosolic O-GlcNAc accumulation and beta-cell death, we treated beta-cell lines HIT-T15 and Min6 with glucosamine. Glucosamine markedly reduced cell viability in both cell lines only at 10 mM. The measurement of cytosolic O-GlcNAc under glucosamine treatment revealed that O-GlcNAc accumulation was observed even at 2 mM glucosamine and maximized at 5 mM, but did not occur very well at 10 mM. Furthermore, 100 microM PUGNAc, an inhibitor of O-GlcNAcase, increased cytosolic O-GlcNAc but did not induce cell death in these cells. Therefore, no correlation between accumulation of cytosolic O-GlcNAc and beta-cell death was suggested. Alternatively, inosine partially rescued cell death induced by glucosamine in Min6 cells, suggesting that energy depletion partly contributes to beta-cell death by glucosamine.

Maximal and submaximal forces of slow fibers in human soleus after bed rest

The effects of 2 and 4 mo of bed rest, with or without exercise countermeasures, on the contractile properties of slow fibers in the human soleus muscle were examined. Mean fiber diameters were 8 and 36% smaller after 2 and 4 mo of bed rest, respectively, than the pre-bed rest level. Maximum tetanic force (P(o)), maximum activated force (F(max)) per cross-sectional area (CSA), and the common-logarithm value of free Ca(2+) concentration required for half-maximal activation (pCa(50)) also decreased after 2 and 4 mo of bed rest. In contrast, maximum unloaded shortening velocity (V(o)) was increased after 2 and 4 mo of bed rest. After 1 mo of recovery, fiber diameters, P(o), F(max) per CSA (P > 0.05), and pCa(50) were increased and V(o) decreased toward pre-bed rest levels. Effects of knee extension/flexion exercise by wearing an anti-G Penguin suit for 10 h daily, and the effects of loading or unloading of the plantar flexors with (Penguin-1) or without (Penguin-2) placing the elastic loading elements of the suit, respectively, were investigated during ~2 mo of bed rest. In the Penguin-1 group, mean fiber diameter, P(o), F(max) per CSA, V(o), and pCa(50) were similar before and after bed rest. However, the responses of fiber size and contractile properties to bed rest were not prevented in the Penguin-2 group, although the degree of the changes was less than those induced by bed rest without any countermeasure. These results indicate that long-term bed rest results in reductions of fiber size, force-generation capacity, and Ca(2+) sensitivity, and enhancement of shortening velocity in slow fibers of the soleus. The data indicate that continuous mechanical loading on muscle, such as stretching of muscle, is an effective countermeasure for the prevention of muscular adaptations to gravitational unloading.

p21(WAF1/Cip1) functions as a suppressor of malignant skin tumor formation and a determinant of keratinocyte stem-cell potential

p21(WAF1/Cip1) is one of the best characterized downstream targets of p53, and the growth suppressing function of this cyclin-dependent kinase inhibitor is well established. However, whether p21 exerts a tumor-suppressing function of its own remains to be established. We report here that, similarly to loss of p53, disruption of the p21(WAF1/Cip1) gene results in a markedly increased susceptibility to chemically induced skin carcinoma formation, whereas the number of papillomas is reduced. Previous evidence indicates that malignant versus benign keratinocyte tumor formation is likely to involve distinct target-cell populations with a different commitment to differentiation. In parallel with the increased susceptibility to carcinoma formation, loss of p21(WAF1/Cip1) was found to promote keratinocyte subpopulations with increased growth/differentiation potential, including clonal growth capability, reversible commitment to differentiation, and capability to generate all types of terminally differentiated keratinocytes present in vivo, not only in the interfollicular epidermis but also in hair follicles. Thus, these findings have revealed a function of p21 as a suppressor of malignant but not benign skin-tumor formation and a determinant of the growth/differentiation potential of keratinocyte subpopulations.